Processing P22 C200 Raster Data

(PIA 7.3.2, March 1999)

This is a step-by-step guide of how to reduce a P22 raster data (staring observation with the 4x4 C200 array detector) from ERD to AAP (equivalent to the AAR, Auto Analysis Result, from the pipeline) with the PIA. The default PIA parameter setting and default flux calibration table are used. If you need more details, please refer to the PIA manual and the IDUM, ISOPHOT Data Users Manual, or contact ISO helpdesk at IPAC.

Select and read Data

Make sure the PIA paths are set up correctly.
[ ] (Top Window) Customize -> PIA paths

Select the P22 file and read it into the PIA buffer. The C200 data files have P2ER prefix.
    [ ] (Top Window) Files -> Files Manager
    [ ] Select File Type: ERD and Detectors: C200.
    [ ] The ERD file name(s) should appear in the "Files" subwindow. If not,
         you can click on one of the subdirectory names shown in the
         "Subdirectories" subwindow to see if you can navigate to the desired file.
         Once you have located the correct file in the "Files" subwindow, click on
         the file name.
    [ ] Click on "Read File" button to read the selected file into the PIA buffer.
    [ ] Option: Click on "Show Header" button to view or to print the ERD FITS
         header.

Normally, one reduces the FCS measurements first then the astronomical data. Every single raster is embraced by two FCS calibrations; hence, there should be two FCS measurements. Both of these should be processed first before the raster measurement. Note that the steps from ERD to SCP are the same regardless of whether the measurement being processed is FCS or astronomical.

Select an ERD measurement for processing.
    [ ] (Top Window) Buffers -> Buffers Manager
    [ ] Select Data Type: ERD and Detectors: C200. All the measurements in the
         selected category should show up in the "measurement" window. There
         should be two FCS measurements. Select the measurement by clicking on it.
    [ ] Click on the "Plot & Reduce Data" button to bring up the PIA ERD window.
    [ ] Option: click on the "Show..." button in the Buffers Manager window to
         view FITS header, Compact Status or even the data values themselves.

Reduction of the ERD (to SRD)

The PIA ERD window shows the read-out ramps as a function of time for all 4 pixels of C200 detector. Some readouts are masked out (shown as red x's) by default.
    [ ] Option: use the "Zoom & Print" button to blow up the displayed pixel in
         order to see individual ramps more clearly or to print the display on the
         laser printer. This option is available on all reduction levels.
    [ ] Option: use the "Selection" button to change the read-out discarding
         scheme from the default.
    [ ] (ERD Window) Correction -> Non-linearity
    [ ] (ERD Window) Correction -> Read-out simple deglitching
         If the number of readouts is too low, the "Test processing (Test
         deglitching)" can be used to reduced the number.
    [ ] (ERD Window) Correction -> 2 Threshold deglitching
    [ ] (ERD Window) Process Meas. -> Fit Ramps (1st order polynomial)
         This fits a slope to each integration ramp and brings up the SRD window.

Reduction of the SRD (to SCP )

The PIA SRD window displays the time series of the ramp slopes for all 4 pixels of C200 detector. Again, the masked out slopes by default are shown in red color.
    [ ] (SRD Window) Correction -> Reset interval correction
    [ ] (SRD Window) Correction -> Deglitching
         This is to filter out badly deviated slopes.
    [ ] (SRD Window) Correction -> Dark Current Subtraction
         This is to subtract out the default orbital position dependent dark
         current.
    [ ] (SRD Window) Process -> no drift handling (Option: with drift handling)
    [ ] Option: (SRD Window) Data -> Save (to PIA internal file)
         This is to save the SRD result.
         This will bring up the SCP window.

Hint: it may be a good idea to process all the measurements in the same AOT to the SCP level before proceeding to the SPD level.

Reduction of the SCP (to AAP)

The PIA SCP window shows the average slopes per chopper plateau as a function of time. This step is slightly different for a FCS measurement than for an astronomical measurement:

If this is an FCS measurement
    [ ] (SCP Window) Correction -> Straylight subtraction (This correction
         is still uncertain, at a level of up to a few percent for C200
         at this point.)
    [ ] (SCP Window) Process -> Responsivity Calculation
         Click on the "ACCEPT" button for the average responsivity value from FCS1.

If this is an astronomical measurement
    [ ] (SCP Window) Process -> Power Calibration (Interpolate Responses)
         This uses a linear interpolation in time between the two FCS measurements.
         Select the FCS measurements on the pop up window and then click the "Ok"
         button. When the PIA Response Menu window appears for each FCS
         measurements, click on the "ACCEPT" button to choose the average
         responsivity values from FCS1. This converts V/s to watts and brings up
         an AAP window.

Hint: in some cases, by concatenating the SRD or SCP results of all the measurements (including the 2 FCS measurements) in the same AOT, one may better judge which of the following is a better way to do flux calibration: interpolation, averaging or simply using only one of the FCS measurements.

Astrophysical Work

    [ ] (Top Window) Buffers -> Astrophysical Work
    [ ] Select "Mapping." The PIA Mapping window appears.
    [ ] (Mapping Window) File -> Select measurement
         Select by clicking on the raster measurement you've processed down to
         the AAP level.
    [ ] (Mapping Window) Process -> Produce map
         Other options under "Process" can be explored.
    [ ] Option: Save your map as a FITS file using the "Save Map..." button to
         the left of the map display.

Last update: 5 March 1999